Heat Recovery and Pressure Control Unit

ABSTRACT

A system for heat recovery and pressure control including: a fresh air heat exchanger with at least one fresh air heat exchanger conduit, a pre-heater heat exchanger with at least one pre-heater heat exchanger conduit, and a proportioning valve coupled to the conduits. The fresh air heat exchanger is adapted to warm the fresh air by transferring heat from the at least one fresh air heat exchanger conduit. The pre-heater heat exchanger is adapted to pre-heat the contaminated air by transferring heat from the at least one pre-heater heat exchanger conduit. The conduits are adapted to receive hot air and transfer heat from the hot air. The proportioning valve is adapted to control the flow of hot air through the conduits.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority to and the benefit of U.S. ProvisionalPatent Application No. 61/080,466, filed on Jul. 14, 2008, in the UnitedStates Patent and Trademark Office, the entire content of which isincorporated herein by reference. The entire content of United Statespatent applications PROCESS AND APPARATUS FOR DRYING AND POWDERIZINGMATERIAL (Attorney Docket No: T643-64003; application Ser. No. ______),ENERGY RECOVERY AND TRANSFER SYSTEM AND PROCESS (Attorney Docket No:T643-63990; application Ser. No. ______), and METHOD AND APPARATUS FORSTERILIZING AND DEODORIZING AIR (Attorney Docket No: T643-64005;application Ser. No. ______) filed on Jul. 14, 2009 in the United StatesPatent and Trademark Office is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates a process and system for heat recovery andpressure control.

BACKGROUND OF THE INVENTION

Animal byproduct meals, fecal material, agricultural fertilizer, cornbyproducts, wheat byproducts, wood pulp, and the like are high moisturecontent materials that may provide a rich source of energy wheneffectively dehydrated. Further, some of this material should besterilized and deodorized before being discharged into the environment.These materials must be dried to about 5% moisture to be a high gradefuel. A large quantity of high temperature air is required to evaporatethe moisture from the material, and the air may become contaminated withodors and pathogens from the material. A great deal of energy isrequired to heat the large quantity of air required. Further, thepressure of the air must be maintained at a suitable pressure.

Therefore, there is a need for a process and system for heat recoveryand pressure control.

SUMMARY OF THE INVENTION

An embodiment of the present invention provides a system for heatrecovery and pressure control. The system includes: a fresh air heatexchanger including a fresh air inlet, at least one fresh air heatexchanger conduit, and a fresh air outlet; a pre-heater heat exchangerincluding a pre-heater inlet, at least one pre-heater heat exchangerconduit, and a pre-heater outlet; and a proportioning valve coupled tothe at least one fresh air heat exchanger conduit and the at least onepre-heater heat exchanger conduit, the proportioning valve including: avalve plate. The fresh air heat exchanger is adapted to receive freshair in the fresh air inlet, warm the fresh air by transferring heat fromthe at least one fresh air heat exchanger conduit, and transmit thewarmed fresh air through the fresh air outlet. The pre-heater heatexchanger is adapted to receive contaminated air in the pre-heaterinlet, pre-heat the contaminated air by transferring heat from the atleast one pre-heater heat exchanger conduit, and transmit the pre-heatedcontaminated air through the pre-heater outlet. The at least one freshair heat exchanger conduit and the at least one pre-heater heatexchanger conduit are adapted to receive hot air and transfer the heatfrom the hot air. The proportioning valve is adapted to control a flowof the hot air through the at least one fresh air heat exchanger conduitand the at least one pre-heater heat exchanger conduit.

At least one of the fresh air heat exchanger further or the pre-heaterheat exchanger may include at least one baffle and at least two passes,wherein the baffle is adapted to increase a length of a path that theair travels through the heat exchanger by guiding the air through the atleast two passes.

The at least one of the fresh air heat exchanger or the pre-heater heatexchanger may further include a gap between the at least one heatexchanger conduit and an interior wall of the heat exchanger.

The system may further include an expansion box adapted to receive hotair and transmit the hot air to the at least one fresh air heatexchanger conduit and the at least one pre-heater heat exchanger conduitin accordance with pressures in the at least one fresh air heatexchanger conduit and the at least one pre-heater heat exchangerconduit.

The proportioning valve may be further adapted to be controlled basedupon at least one of the temperatures of the fresh air exiting the freshair heat exchanger or the temperature of the contaminated air exitingthe pre-heater heat exchanger in accordance with a measurement of atemperature of the fresh air or a measurement of a temperature of thecontaminated air.

At least one of the fresh air heat exchanger and the pre-heater heatexchanger may further include a heat exchanger conduit plate attached toan end of the at least one heat exchanger conduit and adapted to receiveat least one gasket around a perimeter of the heat exchanger conduitplate so that an air-tight seal is maintained between the heat exchangerconduit plate and an interior wall of the heat exchanger as the heatexchanger conduit plate moves along the interior wall of the heatexchanger in accordance with an increase or decrease in a length of theat least one heat exchanger conduit.

Another embodiment of the present invention provides a method for heatrecovery and pressure control. The method includes: receiving fresh airin a fresh air inlet of a fresh air heat exchanger, warming the freshair by transferring heat from at least one fresh air heat exchangerconduit, and transmitting the warmed fresh air through a fresh airoutlet; receiving contaminated air in a pre-heater inlet of a pre-heaterheat exchanger, pre-heating the contaminated air by transferring heatfrom at least one pre-heater heat exchanger conduit, and transmittingthe pre-heated contaminated air through a pre-heater outlet; receivinghot air in the at least one fresh air heat exchanger conduit and the atleast one pre-heater heat exchanger conduit and transferring the heatfrom the hot air; and controlling the flow of the hot air through the atleast one fresh air heat exchanger conduit and the at least onepre-heater heat exchanger conduit by adjusting a proportioning valve.

The method may further include guiding the air around at least onebaffle and through at least two passes in at least one of the fresh airheat exchanger and the pre-heater heat exchanger so that a length of apath traveled by the air is increased.

The method may further include passing the air through a gap between atleast one of the at least one fresh air heat exchanger conduit and aninterior wall of the fresh air heat exchanger, and the at least onepre-heater heat exchanger conduit and an interior wall of the pre-heaterheat exchanger.

The method may further include receiving the hot air in an expansion boxand transmitting the hot air to the at least one fresh air heatexchanger conduit and the at least one pre-heater heat exchanger conduitin accordance with pressures in the at least one fresh air heatexchanger conduit and the at least one pre-heater heat exchangerconduit.

The method may further include controlling the temperature of the freshair exiting the fresh air heat exchanger and the temperature of thecontaminated air exiting the pre-heater heat exchanger by adjusting theproportioning valve.

The method may further include maintaining an air-tight seal between atleast one of a fresh air heat exchanger conduit plate and an interiorwall of the fresh air heat exchanger, and a pre-heater heat exchangerconduit plate and an interior wall of the pre-heater heat exchanger, asthe heat exchanger conduit plate moves along the interior wall of theheat exchanger in accordance with an increase or decrease in a length ofthe at least one heat exchanger conduit.

Another embodiment of the present invention provides a system for heatrecovery and pressure control. The system includes: a heat exchangerincluding an air inlet; at least one heat exchanger conduit; a heatexchanger conduit plate attached to an end of the at least one heatexchanger conduit and adapted to receive at least one gasket around aperimeter of the heat exchanger conduit plate; and an air outlet. Anair-tight seal is maintained between the heat exchanger conduit plateand an interior wall of the heat exchanger as the heat exchanger conduitplate moves along the interior wall of the heat exchanger in accordancewith an increase or decrease in a length of the at least one heatexchanger conduit.

The heat exchanger may further include at least one baffle and at leasttwo passes, wherein the baffle is adapted to increase a length of a paththat the air travels through the heat exchanger by guiding the airthrough the at least two passes.

The heat exchanger may further include a gap between the at least oneheat exchanger conduit and an interior wall of the heat exchanger.

The system may further include an expansion box adapted to receive hotair and transmit the hot air to the at least one heat exchanger conduitin accordance with a pressure in the at least one air heat exchangerconduit.

The system may further include a proportioning valve adapted to controlthe temperature of the air exiting the heat exchanger.

Another embodiment of the present invention provides a method for heatrecovery and pressure control. The method includes: receiving air in anair inlet of a heat exchanger, warming the air by transferring heat fromat least one heat exchanger conduit, and transmitting the warmed airthrough the air outlet; receiving hot air in the at least one heatexchanger conduit and transferring the heat from the hot air. The heatexchanger includes a heat exchanger conduit plate attached to an end ofthe at least one heat exchanger conduit and adapted to receive at leastone gasket around a perimeter of the heat exchanger conduit plate sothat an air-tight seal is maintained between the heat exchanger conduitplate and an interior wall of the heat exchanger as the heat exchangerconduit plate moves along the interior wall of the heat exchanger inaccordance with an increase or decrease in a length of the at least oneheat exchanger conduit.

The method may further include guiding the air around at least onebaffle and through at least two passes in the heat exchanger so that alength of a path traveled by the air is increased.

The method may further include passing the air through a gap between theat least one exchanger conduit and an interior wall of the heatexchanger so that the air expands in the gap.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a system for heat recovery and pressurecontrol according to an embodiment of the present invention.

FIG. 2 is another perspective view of a system for heat recovery andpressure control according to an embodiment of the present invention.

FIG. 3 is another perspective view of a system for heat recovery andpressure control according to an embodiment of the present invention.

FIG. 4 is a cross-sectional perspective view of a system for heatrecovery and pressure control according to an embodiment of the presentinvention (with only some tubes shown for clarity).

FIG. 5 is a cross-sectional top view of a fresh air heat exchangeraccording to an embodiment of the present invention (with only sometubes shown for clarity).

FIG. 6 is a cross-sectional perspective view of a pre-heater heatexchanger according to an embodiment of the present invention (with onlysome tubes shown for clarity).

FIG. 7 is a side view of end tube plates according to an embodiment ofthe present invention.

FIG. 8 is a perspective view of a fresh air cold end tube plate (withonly some tubes shown for clarity) according to an embodiment of thepresent invention.

FIG. 9 is a cross-sectional side view of a proportioning valve accordingto an embodiment of the present invention.

FIG. 10 is a side view of an end tube plate and heat exchanger tubes(with only some tubes shown for clarity) according to an embodiment ofthe present invention.

FIG. 11 is flow chart of a process for heat recovery and pressurecontrol according to an embodiment of the present invention.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the drawingsis intended as a description of embodiments of a process and system forheat recovery and pressure control in accordance with the presentinvention and is not intended to represent the only forms in which theinvention may be constructed or utilized. It is to be understood thatthe same or equivalent functions and structures may be accomplished bydifferent embodiments that are also intended to be encompassed withinthe spirit and scope of the invention. As denoted elsewhere herein, likeelement numbers indicate like elements or features.

Material that must be dried to be a high grade fuel requires a largequantity of high temperature air to evaporate the moisture from thematerial, and the air may become contaminated with odors and pathogensfrom the material. Since a great deal of energy is necessary to heat thelarge quantity of air required, a system and process for capturing andreusing some of this energy would make the processing of this materialmore efficient. Further, the pressure of the air throughout theprocessing of the material should be maintained at a suitable pressure.

A process according to an embodiment of the present invention as shownin FIG. 11 provides a method for heat recovery and pressure control.Here, fresh air is warmed in a heat recovery and pressure control unit100. The warm fresh air and the material to be processed are fed into aprocessor where the air may become contaminated 110. The contaminatedair is then returned to the heat recovery and pressure control unit tobe pre-heated 120. However, the contaminated air is contained away fromthe fresh air that is being warmed.

The pre-heated contaminated air passes to a chamber to be heated 130.Here, for example, the chamber, such as a heating detoxificationchamber, heats the contaminated air to a sufficient temperature tosterilize and deodorize the air.

The hot chamber discharge air passes back to the heat recovery andpressure control unit to be utilized to pre-heat contaminated airentering the chamber and warm fresh air entering the processor 140.Because the chamber discharge air has already been heated, e.g.,sterilized and deodorized, the chamber discharge air is contained awayfrom the contaminated air and the fresh air.

A system for heat recovery and pressure control according to anembodiment of the invention as shown in FIGS. 1-10 includes a fresh airheat exchanger 14, a pre-heater heat exchanger 16, and a proportioningvalve 20 that controls hot air flow through the fresh air heat exchanger14 and the pre-heater heat exchanger 16.

Here, fresh air enters the fresh air heat exchanger 14 through a freshair inlet 32. For example, a fresh air fan 12 may blow fresh air intothe fresh air heat exchanger 14. The fresh air passes through the freshair heat exchanger 14, where the fresh air is warmed, and exits thefresh air heat exchanger through a fresh air outlet 26.

In an embodiment of the present invention as shown in FIG. 5, the freshair passes around at least one fresh air baffle 62, which increases thelength of the path of the fresh air through the fresh air heat exchanger14 and the time that the fresh air is in the fresh air heat exchanger14. Because the fresh air is in the fresh air heat exchanger 14 for alonger time, more heat may be transferred to the fresh air.

In an embodiment of the present invention, the fresh air passes around anumber of or series of (e.g., six) fresh air baffles, which will formmultiple (e.g., seven cross) passes for the fresh air.

In an embodiment of the present invention, the fresh air is warmed to atemperature in a range from about 600 degrees C. to about 650 degrees C.

In an embodiment of the present invention, the fresh air then passesinto a processor where the fresh air is utilized to remove moisture froma material. Here, the fresh air may become contaminated by the material.

The contaminated air is returned to the system and passes into thepre-heater heat exchanger 16 through a pre-heater inlet 34. For example,a contaminated air fan 10 may blow the contaminated air into thepre-heater heat exchanger 16. The contaminated air passes through thepre-heater heat exchanger 16, where the contaminated air is pre-heated,and exits the pre-heater heat exchanger through a pre-heater outlet 28.However, because the contaminated air is contaminated, the contaminatedair is contained away from the fresh air so that the fresh air is notcontaminated.

In an embodiment of the present invention as shown in FIG. 6, thecontaminated air passes around at least one pre-heater baffle 60, whichincreases the length of the path of the contaminated air through thepre-heater heat exchanger 14 and the time that the contaminated air isin the pre-heater heat exchanger 14. Because the contaminated air is inthe pre-heater heat exchanger 14 for a longer time, more heat may betransferred to the contaminated air.

In an embodiment of the present invention, the contaminated air passesaround a number of or series of (e.g., six) fresh air baffles, whichwill form multiple (e.g., seven) cross passes for the contaminated air.

In an embodiment of the present invention, the contaminated air entersthe pre-heater heat exchanger 16 at a temperature of about 120 degreesC. and is pre-heated to a temperature of about 450 degrees C.

In an embodiment of the present invention, the heat exchangers areformed of a corrosion-resistant and heat-resistant material (e.g.,stainless steel).

In an embodiment of the present invention, the contaminated air thenpasses into a chamber, such as a heating detoxification chamber, wherethe contaminated air is heated. For example, the contaminated air may beheated to a high enough temperature (or so that the contaminated air ishot enough) to sterilize and deodorize the air, e.g., a temperature in arange from about 800 degrees C. to about 850 degrees C.

The hot air passes back to the system through a conduit 30 and into anexpansion box 25. Here, the hot air is allowed to enter either at leastone fresh air heat exchanger tube (or suitable conduit) 70 or at leastone pre-heater heat exchanger tube 72, in accordance with the pressurein the at least one fresh air heat exchanger tube (or suitable conduit)70 and the at least one pre-heater heat exchanger tube 72.

The at least one fresh air heat exchanger tube 70 is mounted in andsealed to a fresh air hot end tube plate 50 at the expansion box 25. Theat least one pre-heater heat exchange tube 72 is mounted in and sealedto a pre-heater hot end tube plate 52 at the expansion box 25, as shownin FIG. 8.

The other end of the at least one fresh air heat exchanger tube 70 ismounted in and sealed to a fresh air cold end tube plate 80, as shown inFIGS. 5 and 8. The other end of the at least one pre-heater exchangetube 72 is mounted in and sealed to a pre-heater cold end tube plate 82,as shown in FIG. 6.

In an embodiment of the present invention, the tubes 70 and 72 mayexpand as hot air is transported through the tubes 70 and 72. As thetubes 70 and 72 expand, the length of the tubes 70 and 72 increase. Forexample, tubes 70 and 72 that are about six meters long may expand about40 mm in length. Here, the lengthening of the tubes 70 and 72 may beaccommodated in the heat exchangers 14 and 16 while maintaining thecontainment of the fresh air and the contaminated air away from the hotair. As shown in FIG. 10, at least one groove 92 along the outsideperimeter of the fresh air cold end tube plate 80 is adapted to mount atleast one gasket. The at least one gasket presses against wall 94 tomaintain an air-tight seal while allowing the fresh air cold end tubeplate 80 to slide along the wall 94 as the at least one fresh air heatexchanger tube 70 lengthens. Therefore, the fresh air is contained awayfrom the hot air. The pre-heater cold end tube plate 82 may have asimilar arrangement.

In an embodiment of the present invention, the tubes 70 and 72 arewelded to the tube plates 50, 52, 80, and 82.

In an embodiment of the present invention, the tubes 70 and 72 have adiameter of about ¾ inch.

In an embodiment of the present invention, the tubes 70 and 72 are aboutsix meters long.

In an embodiment of the present invention, the tubes 70 and 72 areformed of stainless steel so that the tubes 70, 72 can withstand hightemperatures and may expand or contract as the tubes 70 and 72 areheated or cooled.

In an embodiment of the present invention, the system has a nest (e.g.,about 1500) of fresh air heat exchanger tubes 70 and a nest (e.g., 1500)of pre-heater heat exchanger tubes 72, with sufficient surface area tocarry out the heat recuperation requirement. For example in anembodiment with a series of baffles, to counter a high pressure drop ofthe cross passes, a gap (or expansion chamber) between the sides of thetubes 70 and 72 and the sides of the heat exchanger 14, 16 may allow theair moving through the heat exchanger 14, 16 to expand and drop invelocity to obtain static regain, thus providing a more uniform air mixto the air moving over the next pass. Therefore, there is a lower totalpressure drop as the air travels through the heat exchanger 14, 16, andthere is a more stable mass flow.

In an embodiment of the present invention, the tubes 70 and 72 aremounted about 5 mm apart.

In an embodiment of the present invention, the temperature of the hotair entering the at least one fresh air heat exchanger tube and the atleast one pre-heater heat exchanger tube is a temperature in a rangefrom about 800 degrees C. to about 850 degrees C.

The interior of the at least one fresh air heat exchanger tube 70 opensinto a manifold that is coupled to conduit 22, and the interior of theat least one pre-heater heat exchanger tube 72 opens into a secondmanifold that is coupled to conduit 24. As shown in FIG. 9, conduits 22and 24 are then coupled to proportioning valve 18, and hot air passesout of the proportioning valve 18 through exit 20. Valve plate 90 insideproportioning valve 18 is adapted to be rotated to control hot air flowthrough tubes 70 and 72. For example, the valve plate 90 may be rotatedso that opening from conduit 22 to exit 20 is decreased and the openingfrom conduit 24 to exit 20 is increased. The pressure in the at leastone fresh air heat exchanger tube 70 will be increased, and the pressurein the at least one pre-heater heat exchanger tube 72 will be decreased.As a result, less hot air enters the at least one fresh air heatexchanger tube 70, and more hot air enters the pre-heater heat exchangertube 72. Therefore, less heat is transferred to the fresh air in thefresh air heat exchanger 14 so the temperature of the warmed fresh airdecreases, and more heat is transferred to the pre-heated contaminatedair in the pre-heater heat exchanger 16 so the temperature of thecontaminated air increases.

In another example, the valve plate 90 may be rotated so that theopening from the conduit 24 to exit 20 is decreased and the opening fromconduit 22 to exit 20 is increased. The pressure in the at least onepre-heater heat exchanger tube 72 will be increased, and the pressure inthe at least one fresh air heat exchanger tube 70 will be decreased. Asa result, less hot air enters the at least one pre-heater heat exchangertube 72 and more hot air enters the at least one fresh air heatexchanger tube 70. Therefore, less heat is transferred to thecontaminated air in the pre-heater heat exchanger 16 so the temperatureof the pre-heated contaminated air decreases, and more heat istransferred to the fresh air in the fresh air heat exchanger 14 so thetemperature of the warmed fresh air increases.

Here, the valve plate 90 may be controlled to maintain a suitabletemperature of the warmed fresh air and or the pre-heated contaminatedair. For example, the temperature of the pre-heated contaminated air maybe measured, and the valve plate 90 may be adjusted accordingly. Thus,if the temperature of the pre-heated contaminated air is too low, thenthe valve plate 90 is rotated so that the opening from the conduit 24 isincreased so that more heat is transferred to the contaminated air, asdescribed above. Therefore, the temperature of the contaminated airincreases. Alternatively, if the temperature of the contaminated air istoo high, then the valve plate 90 is rotated so that the opening fromthe conduit 24 is decreased so that less heat is transferred to thecontaminated air, as described above. Therefore, the temperature of thecontaminated air decreases.

In another example, the temperature of the warmed fresh air may bemeasured, and the valve plate 90 may be adjusted accordingly. Thus, ifthe temperature of the warmed fresh air is too low, then the valve plate90 is rotated so that the opening from the conduit 22 is increased sothat more heat is transferred to the fresh air, as described above.Therefore, the temperature of fresh air increases. Alternatively, if thetemperature of the fresh air is too high, then the valve plate 90 isrotated so that the opening from the conduit 22 is decreased so thatless heat is transferred to the fresh air, as described above.Therefore, the temperature of the fresh air decreases.

In an embodiment of the present invention, the valve plate 90 may becontrolled by an automated process.

In an embodiment of the present invention, the temperatures of the freshair, the contaminated air, and the hot air may be measured at anysuitable location, e.g., any suitable location where the air istransferred.

In another embodiment of the present invention, the temperature of thehot air may be adjusted in accordance with a measurement of thetemperature of the fresh air and/or the contaminated air.

In an embodiment of the present invention, the air leaving the tubes 70and 72 is about 120 degrees C.

In an embodiment of the present invention, the velocity of the airleaving the exit 20 is about 5000 feet per minute.

Although the present invention has been described through the use ofexemplary embodiments, it will be appreciated by those of skill in theart that various modifications may be made to the described embodimentsthat fall within the scope and spirit of the invention as defined by theclaims and their equivalents appended hereto. For example, aspects shownabove with particular embodiments may be combined with or incorporatedinto other embodiments.

1. A system for heat recovery and pressure control, the systemcomprising: a fresh air heat exchanger comprising a fresh air inlet, atleast one fresh air heat exchanger conduit, and a fresh air outlet; apre-heater heat exchanger comprising a pre-heater inlet, at least onepre-heater heat exchanger conduit, and a pre-heater outlet; and aproportioning valve coupled to the at least one fresh air heat exchangerconduit and the at least one pre-heater heat exchanger conduit, theproportioning valve comprising: a valve plate, wherein the fresh airheat exchanger is adapted to receive fresh air in the fresh air inlet,warm the fresh air by transferring heat from the at least one fresh airheat exchanger conduit, and transmit the warmed fresh air through thefresh air outlet, wherein the pre-heater heat exchanger is adapted toreceive contaminated air in the pre-heater inlet, pre-heat thecontaminated air by transferring heat from the at least one pre-heaterheat exchanger conduit, and transmit the pre-heated contaminated airthrough the pre-heater outlet; wherein the at least one fresh air heatexchanger conduit and the at least one pre-heater heat exchanger conduitare adapted to receive hot air and transfer the heat from the hot air,and wherein the proportioning valve is adapted to control a flow of thehot air through the at least one fresh air heat exchanger conduit andthe at least one pre-heater heat exchanger conduit.
 2. The system ofclaim 1, wherein at least one of the fresh air heat exchanger further orthe pre-heater heat exchanger comprises at least one baffle and at leasttwo passes, wherein the baffle is adapted to increase a length of a paththat the air travels through the heat exchanger by guiding the airthrough the at least two passes.
 3. The system of claim 2, wherein theat least one of the fresh air heat exchanger or the pre-heater heatexchanger further comprises a gap between the at least one heatexchanger conduit and an interior wall of the heat exchanger.
 4. Thesystem of claim 1 further comprising an expansion box adapted to receivehot air and transmit the hot air to the at least one fresh air heatexchanger conduit and the at least one pre-heater heat exchanger conduitin accordance with pressures in the at least one fresh air heatexchanger conduit and the at least one pre-heater heat exchangerconduit.
 5. The system of claim 1, wherein the proportioning valve isfurther adapted to be controlled based upon at least one of thetemperatures of the fresh air exiting the fresh air heat exchanger orthe temperature of the contaminated air exiting the pre-heater heatexchanger in accordance with a measurement of a temperature of the freshair or a measurement of a temperature of the contaminated air.
 6. Thesystem of claim 1, wherein at least one of the fresh air heat exchangerand the pre-heater heat exchanger further comprises a heat exchangerconduit plate attached to an end of the at least one heat exchangerconduit and adapted to receive at least one gasket around a perimeter ofthe heat exchanger conduit plate so that an air-tight seal is maintainedbetween the heat exchanger conduit plate and an interior wall of theheat exchanger as the heat exchanger conduit plate moves along theinterior wall of the heat exchanger in accordance with an increase ordecrease in a length of the at least one heat exchanger conduit.
 7. Amethod for heat recovery and pressure control, the method comprising:receiving fresh air in a fresh air inlet of a fresh air heat exchanger,warming the fresh air by transferring heat from at least one fresh airheat exchanger conduit, and transmitting the warmed fresh air through afresh air outlet; receiving contaminated air in a pre-heater inlet of apre-heater heat exchanger, pre-heating the contaminated air bytransferring heat from at least one pre-heater heat exchanger conduit,and transmitting the pre-heated contaminated air through a pre-heateroutlet; receiving hot air in the at least one fresh air heat exchangerconduit and the at least one pre-heater heat exchanger conduit andtransferring the heat from the hot air; and controlling the flow of thehot air through the at least one fresh air heat exchanger conduit andthe at least one pre-heater heat exchanger conduit by adjusting aproportioning valve.
 8. The method of claim 7 further comprising guidingthe air around at least one baffle and through at least two passes in atleast one of the fresh air heat exchanger and the pre-heater heatexchanger so that a length of a path traveled by the air is increased.9. The method of claim 8 further comprising passing the air through agap between at least one of the at least one fresh air heat exchangerconduit and an interior wall of the fresh air heat exchanger, and the atleast one pre-heater heat exchanger conduit and an interior wall of thepre-heater heat exchanger.
 10. The method of claim 7 further comprisingreceiving the hot air in an expansion box and transmitting the hot airto the at least one fresh air heat exchanger conduit and the at leastone pre-heater heat exchanger conduit in accordance with pressures inthe at least one fresh air heat exchanger conduit and the at least onepre-heater heat exchanger conduit.
 11. The method of claim 7 furthercomprising controlling the temperature of the fresh air exiting thefresh air heat exchanger and the temperature of the contaminated airexiting the pre-heater heat exchanger by adjusting the proportioningvalve.
 12. The method of claim 7 further comprising maintaining anair-tight seal between at least one of a fresh air heat exchangerconduit plate and an interior wall of the fresh air heat exchanger, anda pre-heater heat exchanger conduit plate and an interior wall of thepre-heater heat exchanger, as the heat exchanger conduit plate movesalong the interior wall of the heat exchanger in accordance with anincrease or decrease in a length of the at least one heat exchangerconduit.
 13. A system for heat recovery and pressure control, the systemcomprising: a heat exchanger comprising an air inlet; at least one heatexchanger conduit; a heat exchanger conduit plate attached to an end ofthe at least one heat exchanger conduit and adapted to receive at leastone gasket around a perimeter of the heat exchanger conduit plate; andan air outlet, wherein an air-tight seal is maintained between the heatexchanger conduit plate and an interior wall of the heat exchanger asthe heat exchanger conduit plate moves along the interior wall of theheat exchanger in accordance with an increase or decrease in a length ofthe at least one heat exchanger conduit.
 14. The system of claim 13,wherein the heat exchanger further comprises at least one baffle and atleast two passes, wherein the baffle is adapted to increase a length ofa path that the air travels through the heat exchanger by guiding theair through the at least two passes.
 15. The system of claim 14, whereinthe heat exchanger further comprises a gap between the at least one heatexchanger conduit and an interior wall of the heat exchanger.
 16. Thesystem of claim 13 further comprising an expansion box adapted toreceive hot air and transmit the hot air to the at least one heatexchanger conduit in accordance with a pressure in the at least one airheat exchanger conduit.
 17. The system of claim 13, further comprising aproportioning valve adapted to control the temperature of the airexiting the heat exchanger.
 18. A method for heat recovery and pressurecontrol, the method comprising: receiving air in an air inlet of a heatexchanger, warming the air by transferring heat from at least one heatexchanger conduit, and transmitting the warmed air through the airoutlet; receiving hot air in the at least one heat exchanger conduit andtransferring the heat from the hot air; and wherein the heat exchangercomprises a heat exchanger conduit plate attached to an end of the atleast one heat exchanger conduit and adapted to receive at least onegasket around a perimeter of the heat exchanger conduit plate so that anair-tight seal is maintained between the heat exchanger conduit plateand an interior wall of the heat exchanger as the heat exchanger conduitplate moves along the interior wall of the heat exchanger in accordancewith an increase or decrease in a length of the at least one heatexchanger conduit.
 19. The method of claim 18 further comprising guidingthe air around at least one baffle and through at least two passes inthe heat exchanger so that a length of a path traveled by the air isincreased.
 20. The method of claim 19 further comprising passing the airthrough a gap between the at least one exchanger conduit and an interiorwall of the heat exchanger so that the air expands in the gap.